Thermodynamic conversion system using gas and air turbines

ABSTRACT

In a combined plant including a gas turbine (1) and an air bottoming gas turbine aggregate (2) which includes air compressors (8) and a turbine (9) coupled thereto, wherein the gas turbine outlet gas is in heat exchange with the compressed air from the compressor (8), the gas turbine (1, 6) and the air turbine (9) are provided with mutually rotary dependent torque shafts (10), so that the plant may be controlled by simply controlling the flow of fuel to the gas turbine.

FIELD OF THE INVENTION

The present invention relates to thermodynamic conversion apparatus.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,751,814 discloses an air cycle thermodynamic conversionsystem including a gas turbine providing a flow of heated gases from thegas turbine exhaust; at least one air compressor for compressing ambientair; a heat exchanger including means for transferring heat from saidflow of heated gas turbine exhaust gases to a compressed air from saidair compressor to produce a heated compressed air; at least one airturbine connected to the heat exchanger responsive to said heatedcompressed air to drive said at least one compressor; said heatedcompressed air including an excess of energy beyond that required bysaid at least one air turbine to drive said at least one air compressor;and, means for delivering said excess of energy to a using process. Byestablishing the heated exhaust gas and the compressed air flow in theheat exchanger such that they both have about equal heat capacities, aminimum temperature gradient is maintained between them. The use ofcompressed air provides an air bottoming cycle.

The control of this known system requires control valves to regulate theflow rate of heated air, and its temperature, to the air turbine inorder to regulate the power developed in the air turbine. This requirescontrol valves of large dimensions and the control system is a slowworking system. Thus no practicable control has been available upto-day. I have now discovered that a desired rapid and convenientcontrol may be provided by establishing mutually rotary dependent torqueaxes of the gas turbine and the air turbine. This new arrangement makesit possible to control the system by only controlling the gas turbine,i.e. by controlling the fuel flow to the combustion chamber of the gasturbine. Control of fuel flow to the combustion chamber results in arapid change of the gas turbine performance and of the total apparatus,due to the dependency of the torque axes of the gas turbine and the airturbine. This rapid control of power output from the gas turbine alsocompensates for the slow-reacting air bottoming cycle due to the largethermal inertia in the heat exchanger.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a thermodynamicconversion system including a gas turbine and which employs an airbottoming cycle for recovering heat energy in a useful form from astream of heated gas.

It is a further object of the invention to provide a control means for asuch thermodynamic conversion system.

A still further object of the invention is to provide a thermodynamicconversion system including a gas turbine and an air bottoming apparatusincluding an air turbine which system is controllable by controlling thegas turbine.

Briefly stated, the present invention provides a thermodynamicconversion system including a gas turbine providing a flow of heatedgases from the gas turbine exhaust, at least one air compressor forcompressing ambient air; a heat exchanger including means fortransferring heat from said flow of heated gas turbine exhaust gases toa compressed air from said air compressor to produce a heated compressedair; at least one air turbine connected to the heat exchanger responsiveto said heated compressed air to drive said at least one compressor;said heated compressed air including an excess of energy beyond thatrequired by said at least one air turbine to drive said at least one aircompressor; and a controlling means controlling the energy supply to thegas turbine, said gas turbine and said air turbine having mutuallyrotary dependent torque axes, so that said controlling of the energysupply to the gas turbine results in simultaneously control of the airturbine and the air compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

FIG. 1 is a schematic diagram of a thermodynamic conversion systemaccording to the prior art.

FIG. 2 is a schematic diagram of a first possible thermodynamicconversion system according to the invention.

FIGS. 3-9 disclose schematic diagrams of a second to an eighth possiblethermodynamic conversion system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a thermodynamic conversion systemaccording to the prior art and including a parent gas turbine 1, an airbottoming cycle gas turbine 2 and a counterflow heat exchanger 3. Theparent gas turbine comprises a compressor 4, a combustion chamber 5, anda turbine 6. The air bottoming cycle gas turbine 2 comprises a series ofthrough intercoolers 7 connected air compressors 8 and an air turbine 9.The compressed air from the compressors 8 flows to the heat exchanger 3and from there to the air turbine 9. Exhaust gases from the gas turbine6 flow to the heat exchanger 3 for counterflow heat exchange with thecompressed air from the air compressors 8. This known thermodynamicconversion apparatus is controlled by controlling the heat exchanger, asdisclosed in U.S. Pat. No. 4,751,814, the content of which is herebyenclosed by reference.

According to this prior art it is known to combine 8 turbine and an aircompressor/turbine combination using exchange between gas turbineexhaust gases and compressed air to provide useful shaft power orprocess heat.

Application of the air bottoming cycle may be where the load on both theparent gas turbine and the air bottoming cycle gas turbine may vary, forexample on an offshore oil and gas production facility. In such anapplication it is important for the operator that a minimum amount ofcontrol, either active or passive, is required. The way the parent gasturbine and the air bottoming cycle gas turbine are configured togetheraccording to the invention has a significant influence on ease ofcontrol and operability.

In the following illustrations and descriptions (FIGS. 2-9), it is theway in which the parent gas turbine and the air bottoming cycle gasturbine are arranged which is of significance.

The air bottoming cycle gas turbine is therefore shown simplified in thecompressor section. It is to be understood that all configurations mayinclude multiple compressors with intercooling.

Also for simplicity, the heat exchanger with interconnection is notshown completely. All configurations will also include these, asdisclosed in FIG. 1.

FIG. 2 shows the simplest combined configuration according to theinvention, a single shaft parent gas turbine 1 directly coupled to asingle shaft air bottoming cycle gas turbine 2, the shaft 10 beingrepresented by the so nominated line. The load is represented by thesquare 11 (The letter L =load).

If the parent gas turbine -PGT- has a shaft out of both ends of themachine, the PGT can be between the air bottoming cycle gas turbine-ABCGT- and the load -L-.

The configuration in FIG. 2 is ideal for driving an electrical generatoror an other constant (and single) speed load device.

The control method is identical with that of a normal single shaft gasturbine, including upset conditions.

FIG. 3 shows a configuration as in FIG. 2, the only difference being theinsertion of gears 12 between the PGT and the ABCGT and the load L,respectively. These gears may be included to enable differing speeds tobe matched. This may be because the PGT and ABCGT naturally havedifferent operational rotational speeds, or because forcing differentspeeds can achieve different performance characteristics which may bedesirable.

FIG. 4 shows a single shaft PGT coupled to one end of the load L and asingle shaft ABCGT coupled to the other end. This configuration can giveflexibility in installation of the air intakes, exhausts and heatexchanges.

FIG. 5 shows the same configuration as in FIG. 4, the difference beingthe use of gears 12 between PGT 1, the load L 11 and the ABCGT 2,respectively.

FIG. 6 is a configuration similar to FIG. 2, but with a two shaft PGT(high and low pressure turbines 6H and 6L).

Correspondingly FIGS. 7, 8, and 9 show a configuration similar to FIGS.2, 4, and 5 respectively, with a two shaft PGT.

Without being shown in the figures, in addition and similarly to any orall of the above configurations, multiple PGTs could be coupled to oneABCGT. Also, multiple ABCGTs could be coupled to one PGT.

I claim:
 1. A thermodynamic conversion system comprising:a gas turbineproviding a flow of heated gases from the gas turbine exhaust; at leastone air compressor for compressing ambient air; a heat exchangerincluding means for transferring heat from said flow of heated gasturbine exhaust gases to compressed air from said air compressor toproduce heated compressed air; at least one air turbine connected to theheat exchanger responsive to said heated compressed air said at leastone compressor, said heated compressed air including an excess of energybeyond that required by said at least one air turbine to drive said atleast one air compressor; at least one of said air compressor and saidair turbine being operatively connected to a load; and said gas turbineand said air turbine having mutually rotary dependent torque shaftsextending along a common axis whereby energy supplied to the gas turbineresults in simultaneous control of said air turbine and said aircompressor.
 2. The thermodynamic conversion system according to claim 1,further comprising a gear connection between said shafts of said gasturbine and said air turbine.
 3. A thermodynamic conversion systemcomprising:a gas turbine providing a flow of heated gases from the gasturbine exhaust; a combustion chamber directly connected to said gasturbine; at least one air compressor for compressing ambient air; a heatexchanger including means for transferring heat from said flow of heatedgas turbine exhaust gases to compressed air from said air compressor toproduce a heated compressed air; at least one air turbine connected tothe heat exchanger responsive to said heated compressed air to drivesaid at least one compressor, said heated compressed air including anexcess of energy beyond that required by said at least one air turbineto drive said at least one air compressor; at least one of said aircompressor and said air turbine being operatively connected to a load;and said gas turbine and said air turbine having mutually rotarydependent torque shafts extending along a common axis whereby energysupplied to the gas turbine results in simultaneous control of said airturbine and said air compressor.
 4. The thermodynamic conversion systemaccording to claim 3, further comprising a gear connection between saidshafts of said gas turbine and said air turbine.